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18 March 2003 <br /> AGE-NC Project No. 97-0333 <br /> Page 2 of 3 <br /> support, the decision was made between AGE and the SJCEHD to select GWE as an interim <br /> remediation method based on the following arguments: (1) permeable lithology to approximately <br /> 45 feet bsg appeared to be ideal conditions for GWE, (2) GWE would implement immediate <br /> hydraulic control,(3) GWE would inhibit further offsite migration of the dissolved petroleum plume <br /> and/or potentially pull some of the off-site ground water plume back towards the site, (4) GWE has <br /> been successfully performed by AGE at a nearby LUST site, approximately 350 feet towards the <br /> north, and(5) GWE would in essence `buy' time, so that off-site migration would not escalate and <br /> a Problem Assessment Report (PAR) and a Remedial Action Plan (RAP) could be adequately <br /> prepared. <br /> SVE/IAS were evaluated during the 17 December 2002 meeting between AGE and the SJCEHD; <br /> however, AGE considered the following arguments for not selecting SVE/IAS as the more <br /> appropriate interim remedial method: (1) AGE had concerns that IAS, in the interim, might <br /> accelerate the offsite migration of the ground water plume, (2) AGE had concerns that IAS would <br /> actually be effective in mechanically stripping hydrocarbons adhered to soil or volatilizing <br /> hydrocarbons in the dissolved ground water plume, (3) AGE had experienced mixed results with <br /> IAS at nearby sites and with similar subsurface conditions, (4) due to a trend of increasing ground <br /> water elevations,the vadose zone has become increasingly narrow, and(5)the rising cost for energy <br /> (i.e. PG&E) to operate SVE units, AGE anticipated that GWE would be a more cost-effective <br /> selection for the interim. <br /> It would appear at this time that both GWE and SVE/IAS are both viable options for interim <br /> remediation at this site. Generally speaking, SVE/IAS are well accepted methods for treatment of <br /> hydrocarbon-impacted soil and ground water; SVE is most effective on volatile hydrocarbons in <br /> permeable soil, and IAS is commonly conducted concurrently with an SVE system In addition, <br /> based on AGE's review of cross sections (A-A' through F-F') generated throughout this site <br /> investigation, a permeable, sandy material is apparent at depths between 12 and 45 feet bsg(vadose <br /> zone and First Water Zone);therefore, SVE/IAS should also be an effective remediation alternative. <br /> At the present time,AGE believes that GWE would be the more effective of the two remediation <br /> technologies for interim remediation, from the standpoints of cost as well as uncertainties regarding <br /> IAS performance. Due to the limited amount of available site-specific data, and because the <br /> CVRWQCB requested that additional GWE supporting evidence and arguments should be submitted <br /> for regulatory review, AGE concurs with the CVRWQCB's recommendation that it would be <br /> appropriate at this time to perform a GWE pumping test prior to selecting the most appropriate <br /> interim remediation method. During well installation,AGE will also conduct soils testing of intrinsic <br /> permeability,moisture content and porosity to further evaluate the overall effectiveness of SVE/IAS. <br /> Advanced GeoEnvirom ental,Inc. <br />